Zephyr Migration Tool - Exception while creating attachments.Method: sendAttachments()

We are getting this error whenever the migration tool attempts to send a binary attachment:

ERROR - c.z.m.s.i.AttachmentServiceImpl - Exception while creating attachments.Method: sendAttachments()
org.springframework.web.client.HttpServerErrorException$InternalServerError: 500 Internal Server Error: [{"errorType":"ERROR","clientMessage":"We encountered some problems during processing this request. Please try again!","errorCode":104}]

This could be png, or Adobe RDF, or any binary content int eh attachment